U.S. patent application number 15/859007 was filed with the patent office on 2018-07-12 for access management to multi-user uplink random resource units by a plurality of bsss.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Stephane BARON, Patrice NEZOU, Pascal VIGER.
Application Number | 20180199271 15/859007 |
Document ID | / |
Family ID | 58463744 |
Filed Date | 2018-07-12 |
United States Patent
Application |
20180199271 |
Kind Code |
A1 |
VIGER; Pascal ; et
al. |
July 12, 2018 |
ACCESS MANAGEMENT TO MULTI-USER UPLINK RANDOM RESOURCE UNITS BY A
PLURALITY OF BSSs
Abstract
A physical Access Point (AP) manages a plurality of BSS groups
through Virtual APs. The AP periodically sends beacon frames
informing of the profile of each BSS of the plurality of BSSs. To
improve channel utilization, the trigger frame identifies a
plurality of BSS groups, stations of which are allowed to access
the resources units to transmit data during the reserved TXOP. The
AP receives, during the reserved TXOP, data from one station of a
first group identified in the trigger frame and data from one
station (separate from the first one) of a second and separate
group identified in the trigger frame. First group and second group
use the same joint set of random access parameters for the random
access procedure, thus ensuring equivalent fairness in accessing
the offered the resources units to transmit data during the
reserved TXOP to several BSSs.
Inventors: |
VIGER; Pascal; (JANZE,
FR) ; BARON; Stephane; (LE RHEU, FR) ; NEZOU;
Patrice; (LIFFRE, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
58463744 |
Appl. No.: |
15/859007 |
Filed: |
December 29, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 88/08 20130101;
H04W 72/1289 20130101; H04W 48/12 20130101; H04W 84/12 20130101;
H04W 74/006 20130101; H04W 74/085 20130101; H04W 92/20 20130101;
H04W 72/121 20130101 |
International
Class: |
H04W 48/12 20060101
H04W048/12; H04W 74/08 20060101 H04W074/08; H04W 72/12 20060101
H04W072/12; H04W 92/20 20060101 H04W092/20 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 10, 2017 |
GB |
1700432.6 |
Claims
1. A wireless communication method in a wireless network comprising
a physical access point and a plurality of stations organized into
groups, each group being managed by a virtual access point
implemented in the physical access point, the method comprising the
following steps, at the physical access point: sending a joint set
of random access parameters to be used in common by stations of the
plurality of groups to contend for access to a random resource unit
included in a transmission opportunity; sending a trigger frame
reserving a transmission opportunity on at least one communication
channel of the wireless network, the transmission opportunity
including random resource units that stations may access using a
contention scheme; and in response to the trigger frame, receiving,
over a random resource unit included in the reserved transmission
opportunity, data from a station of one of the plurality of
groups.
2. The method of claim 1, wherein the joint set of random access
parameters is included in a beacon frame, separate from the trigger
frame, sent by the physical access point.
3. The method of claim 2, wherein a plurality of sets of random
access parameters are sent by the physical access point in one or
more beacon frames, each set being associated with one group for
use by the stations of that group to contend for access to random
resources units of a transmission opportunity reserved by a trigger
frame for the stations of the group.
4. The method of claim 3, wherein each set of random access
parameters is sent in a separate beacon frame by the virtual access
point, implemented in the physical access point, which manages the
group of stations associated with the set.
5. The method of claim 3, wherein a plurality of sets of random
access parameters are sent by the physical access point in one
beacon frame.
6. The method of claim 3, wherein the joint set of random access
parameters is one of the plurality of sets of random access
parameters.
7. The method of claim 6, wherein at least one beacon frame
includes an indication indicating which one of the plurality of
sets is to be used as the joint set of random access
parameters.
8. The method of claim 6, wherein the joint set of random access
parameters is the set of random access parameters of the virtual
access point identified as the transmitter of the beacon frame.
9. The method of claim 1, wherein each group is uniquely identified
by a specific basic service set identification, BSSID.
10. The method of claim 9 wherein the sent trigger frame includes a
list of BSSIDs identifying the plurality of groups, stations of
which are allowed to contend for access to the random resources
units of the transmission opportunity reserved by the trigger
frame.
11. The method of claim 10, wherein each BSSID is derived from a
base BSSID specific to the physical access point.
12. The method of claim 11, wherein the BSSID field is n-bit long,
where n is the number of bits varying between the BSSIDs compared
to the base BSSID.
13. The method of claim 1, wherein a set of random access
parameters includes a lower boundary OCW.sub.min and/or higher
boundary OCW.sub.max, both defining a selection range from which a
size of a contention window OCW for random access is selected.
14. A wireless communication method in a wireless network
comprising a physical access point and a plurality of stations
organized into groups, each group being managed by a virtual access
point implemented in the physical access point, the method
comprising the following steps, at one station belonging to a first
group: obtaining a joint set of random access parameters to be used
in common by stations of the first group and a second group to
contend for access to a random resource unit included in a
transmission opportunity; receiving a trigger frame from the
physical access point, the trigger frame reserving a transmission
opportunity on at least one communication channel of the wireless
network, the transmission opportunity including random resource
units that the stations may access using a contention scheme, the
trigger frame identifying the first group, stations of which are
allowed to contend for access to random resources units included in
the transmission opportunity to transmit data; and contending for
access to a random resource unit, included in the reserved
transmission opportunity, using the obtained joint set of random
access parameters.
15. The method of claim 14, wherein a set of random access
parameters includes a lower boundary OCW.sub.min and/or higher
boundary OCW.sub.max, both defining a selection range from which a
size of a contention window OCW for random access is selected.
16. The method of claim 15, wherein the contention scheme at the
station decrements a backoff value OBO of a backoff counter
initially drawn in the range, zero to OCW, of the contention window
for random access, and triggers access to a random resource unit in
the transmission opportunity upon the backoff value reaching a
target value.
17. The method of claim 14, wherein the joint set of random access
parameters is obtained from a beacon frame, separate from the
trigger frame, received from the physical access point.
18. The method of claim 17, wherein a plurality of sets of random
access parameters are received from the physical access point in
one or more beacon frames, each set being associated with one group
for use by the stations of that group to contend for access to
random resources units of a transmission opportunity reserved by a
trigger frame for the stations of the group.
19. The method of claim 18, wherein each set of random access
parameters is sent by the physical access point in a separate
beacon frame of the virtual access point managing the group of
stations associated with the set.
20. The method of claim 18, wherein the joint set of random access
parameters is one of the plurality of sets of random access
parameters.
21. The method of claim 20, wherein at least one beacon frame
includes an indication indicating which one of the plurality of
sets is to be used as the joint set of random access
parameters.
22. The method of claim 21, wherein the joint set of random access
parameters is the set of random access parameters of the virtual
access point identified as the transmitter of the beacon frame.
23. The method of claim 14, wherein each group is uniquely
identified by a specific basic service set identification,
BSSID.
24. The method of claim 23, wherein each BSSID is derived from a
base BSSID specific to the physical access point.
25. The method of claim 24, wherein the set associated with the
group identified by the base BSSID is selected as the joint set of
random access parameters.
26. The method of claim 18, wherein the joint set of random access
parameters is selected among the plurality of sets based on a
predefined rule known to stations of the first and the second
group.
27. A physical access point in a wireless network comprising a
plurality of stations organized into groups, each group being
managed by a virtual access point implemented in the physical
access point, the physical access point comprising: at least one
microprocessor configured for carrying out the following steps:
sending a joint set of random access parameters to be used in
common by stations of the plurality of groups to contend for access
to a random resource unit included in a transmission opportunity;
sending a trigger frame reserving a transmission opportunity on at
least one communication channel of the wireless network, the
transmission opportunity including random resource units that
stations may access using a contention scheme; and in response to
the trigger frame, receiving, over a random resource unit included
in the reserved transmission opportunity, data from a station of
one of the plurality of groups.
28. A station device in a wireless network comprising a physical
access point and a plurality of stations organized into groups,
each group being managed by a virtual access point implemented in
the physical access point, the station, belonging to a first group,
comprising: at least one microprocessor configured for carrying out
the following steps: obtaining a joint set of random access
parameters to be used in common by stations of the first group and
a second group to contend for access to a random resource unit
included in a transmission opportunity; receiving a trigger frame
from the physical access point, the trigger frame reserving a
transmission opportunity on at least one communication channel of
the wireless network, the transmission opportunity including random
resource units that the stations may access using a contention
scheme, the trigger frame identifying the first group, stations of
which are allowed to contend for access to random resources units
included in the transmission opportunity to transmit data; and
contending for access to a random resource unit, included in the
reserved transmission opportunity, using the obtained joint set of
random access parameters.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit under 35 U.S.C. .sctn.
119(a)-(d) of United Kingdom Patent Application No. 1700432.6,
filed on Jan. 10, 2017 and entitled "Improved access management to
multi-user uplink random resource units by a plurality of BSSs".
The above cited patent application is incorporated herein by
reference in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to communication
networks and more specifically to the sending of data over a
communication channel which is split into sub-channels (or Resource
Units) that are available to groups of stations associated with a
respective plurality of network cells.
[0003] The invention finds application in wireless communication
networks, in particular to the access of an 802.11ax composite
channel and of OFDMA Resource Units forming for instance an
802.11ax composite channel for Uplink communication. One
application of the method regards wireless data communication over
a wireless communication network using Carrier Sense Multiple
Access with Collision Avoidance (CSMA/CA), the network being
accessible by a plurality of station devices.
BACKGROUND OF THE INVENTION
[0004] The IEEE 802.11 MAC family of standards (a/b/g/n/ac/etc.)
define a way wireless local area networks (WLANs) must work at the
physical and medium access control (MAC) level. Typically, the
802.11 MAC (Medium Access Control) operating mode implements the
well-known Distributed Coordination Function (DCF) which relies on
a contention-based mechanism based on the so-called "Carrier Sense
Multiple Access with Collision Avoidance" (CSMA/CA) technique.
[0005] More recently, Institute of Electrical and Electronics
Engineers (IEEE) officially approved the 802.11ax task group, as
the successor of 802.11ac. The primary goal of the 802.11ax task
group consists in seeking for an improvement in data speed to
wireless communicating devices used in dense deployment
scenarios.
[0006] In this context, multi-user (MU) transmission has been
considered to allow multiple simultaneous transmissions to/from
different users in both downlink (DL) and uplink (UL) directions
from/to the AP and during a transmission opportunity granted to the
AP. In the uplink, multi-user transmissions can be used to mitigate
the collision probability by allowing multiple non-AP stations to
simultaneously transmit. To actually perform such multi-user
transmission, it has been proposed to split a granted communication
channel into sub-channels, also referred to as resource units
(RUs), that are shared in the frequency domain by multiple users
(non-AP stations/nodes), based for instance on Orthogonal Frequency
Division Multiple Access (OFDMA) technique.
[0007] The above is introduced with respect to a single group of
stations that is managed by the access point with which each
station has previously registered. In the 802.11 standard, such a
group of stations together with the access point is known as a
Basic Service Set (BSS). The access point acts as a master to
control the stations within the BSS. The simplest BSS consists of
one access point and one station.
[0008] Each BSS is uniquely identified by a specific basic service
set identification, BSSID. For a BSS operating in infrastructure
mode, the specific BSSID is usually a 48-bit MAC address of the
access point. The specific BSSID is the formal name of the BSS and
is always associated with only one BSS.
[0009] Together with the specific BSSID, each BSS has its own
service set identification, SSID, which is the informal (human)
name of the BSS (since this own SSID identifier is often entered
into devices manually by a human user).
[0010] In a BSS, the stations usually contend for access to the
communication medium as described above.
[0011] Recent developments provide that a single physical AP can
operate as the master stations of a plurality of BSSs, i.e. of a
plurality of independent groups of stations. This avoids using one
physical AP per BSS or WLAN. It also makes it possible to use the
same primary channel for all BSSs, thereby avoiding channel
interference problems.
[0012] Such operating scheme where a plurality of BSSs is managed
by the same physical AP is performed through so-called virtual
access points (virtual APs or VAPs).
[0013] A Virtual AP is a logical entity that resides within a
physical Access Point (AP). To a client, the VAP appears as an
independent access point with its own unique SSID. To implement
virtual APs, multiple BSSIDs are used with associated SSIDs. The
BSSIDs for the VAPs in the physical AP are usually generated from a
base BSSID specific to the underlying physical AP, usually the base
MAC address of the AP.
[0014] The terms Virtual AP, specific BSSID, BSS and SSID can be
used synonymously throughout this document, to designate a group or
cell of stations managed by a physical AP. Depending on the
context, specific BSSID and own SSID may further refer to the
identifier of a BSS/WLAN, either through a MAC address (specific
BSSID) or an informal (human) name (own SSID).
[0015] Providing a plurality of SSIDs (or BSS) corresponds to
providing various different networks in a particular area. It can
give access to different resources and present services which may
have differing management or security policies applied. This
advantageously allows various categories of user, e.g. staff,
students or visitors etc. to be provided with network services
which are appropriate to them.
[0016] In conventional 802.11 approaches, only one SSID (or BSS) is
advertised per signaling message such as a beacon frame. As a
consequence, multiple beacons are used to advertise the SSIDs
corresponding to the virtual APs configured at the physical AP.
This solution is compatible with most 802.11 stations and also
allows the SSIDs to support different capability sets.
[0017] However, as the number of BSSs increases, more channel
utilization results from such signaling. This downside is further
increased because the signaling messages are transmitted at low bit
rate, usually at the lowest supported data rate so that all clients
can receive it.
[0018] To improve this situation of increased channel utilization
in case of multiple BSSs, the IEEE 802.11v Wireless Network
Management specification defines a mechanism to advertise multiple
security profiles including BSSID/SSID advertisements, with a
single beacon frame.
[0019] However, the resulting network management is not
satisfactory. In particular, the medium access for uplink
communication through trigger frames using contention access is
performed independently for each BSS and the support for multi-BSS
Trigger frames is not provided.
SUMMARY OF INVENTION
[0020] It is a broad objective of the present invention to improve
this situation, i.e. to overcome some or all of the foregoing
limitations. In particular, the present invention seeks to provide
a more efficient usage of the UL MU random access procedure in case
of multiple BSS group.
[0021] In this context, the present invention proposes, according
to a first aspect, a wireless communication method in a wireless
network comprising a physical access point and a plurality of
stations organized into groups, each group being managed by a
virtual access point implemented in the physical access point. The
method comprising the following steps, at the physical access
point:
[0022] sending a trigger frame reserving a transmission opportunity
on at least one communication channel of the wireless network, the
transmission opportunity including random resource units that the
stations may access using a contention scheme, the trigger frame
identifying a plurality of groups, stations of which are allowed to
contend for access to the random resources units included in the
transmission opportunity to transmit data;
[0023] sending a joint set of random access parameters to be used
in common by stations of the plurality of groups identified in the
trigger frame to contend for access to a random resource unit
included in the transmission opportunity; and
[0024] in response to the trigger frame, receiving, over the random
resource unit, data from a station of one of the plurality of
identified groups identified in the trigger frame.
[0025] Correspondingly, the invention also regards a physical
access point in a wireless network comprising a plurality of
stations organized into groups, each group being managed by a
virtual access point implemented in the physical access point. The
physical access point comprising:
[0026] at least one microprocessor configured for carrying out the
following steps:
[0027] sending a trigger frame reserving a transmission opportunity
on at least one communication channel of the wireless network, the
transmission opportunity including random resource units that the
stations may access using a contention scheme, the trigger frame
identifying a plurality of groups, stations of which are allowed to
contend for access to the random resources units included in the
transmission opportunity to transmit data;
[0028] sending a joint set of random access parameters to be used
in common by stations of the plurality of groups identified in the
trigger frame to contend for access to a random resource unit
included in the transmission opportunity; and
[0029] in response to the trigger frame, receiving, over the random
resource unit, data from a station of one of the plurality of
identified groups identified in the trigger frame.
[0030] In one implementation, the joint set of random access
parameters is included in the trigger frame. This advantageously
provides highly interactive adaptation of the parameter set upon
each trigger frame.
[0031] In one implementation, the joint set of random access
parameters is included in a beacon frame, separate from the trigger
frame, sent by the physical access point. Advantageously, the
groups are advertised in advance from the further usage, and the
stations have time to memorize various group contexts. It saves
also overhead than when trigger frames are used, which are more
frequent than beacon frames.
[0032] In one implementation, a plurality of sets of random access
parameters are sent by the physical access point in one or more
beacon frames, each set being associated with one group for use by
the stations of that group to contend for access to random
resources units of a transmission opportunity reserved by a trigger
frame for the stations of the group. This allow an AP to set and
finely tune individual parameters for each group (according
encountered contention, number of stations, etc.).
[0033] In one implementation, each set of random access parameters
is sent in a separate beacon frame by the virtual access point,
implemented in the physical access point, which manages the group
of stations associated with the set. This allows to maintain
backward compatibility of legacy stations.
[0034] In one implementation, a plurality of sets of random access
parameters are sent by the physical access point in one beacon
frame. This reduces overhead in wireless medium (one transmission
instead of a lot of beacons).
[0035] In one implementation, the joint set of random access
parameters is additional to the plurality of sets and is included
in one of the beacon frames. Consequently, the joint set is clearly
advertised to the stations, according a legacy method (either
individual beacons or a mutli-BSS beacon).
[0036] In one implementation, the joint set of random access
parameters is one of the plurality of sets of random access
parameters. This reduces the overhead in beacon body.
[0037] In one implementation, at least one beacon frame includes an
indication indicating which one of the plurality of sets is to be
used as the joint set of random access parameters.
[0038] In one implementation, the trigger frame includes an
indication indicating which one of the plurality of sets is to be
used as the joint set of random access parameters.
[0039] In one implementation, the joint set of random access
parameters is the set of random access parameters of the virtual
access point identified as the transmitter of the beacon frame.
This makes the transmitted BSS the reference for random access
parameters.
[0040] In one implementation, each group is uniquely identified by
a specific basic service set identification, BSSID.
[0041] In one implementation, the sent trigger frame includes a
list of BSSIDs identifying the plurality of groups, stations of
which are allowed to contend for access to the random resources
units of the transmission opportunity reserved by the trigger
frame.
[0042] In one implementation, each BSSID is derived from a base
BSSID specific to the physical access point.
[0043] In one implementation, the BSSID field is n-bit long, where
n is the number of bits varying between the BSSIDs compared to the
base BSSID.
[0044] In one implementation, a set of random access parameters
includes a lower boundary OCWmin and/or higher boundary OCWmax,
both defining a selection range from which a size of a contention
window OCW for random access is selected.
[0045] The present invention proposes, according to a second
aspect, a wireless communication method in a wireless network
comprising a physical access point and a plurality of stations
organized into groups, each group being managed by a virtual access
point implemented in the physical access point. The method
comprising the following steps, at one station belonging to a first
group:
[0046] receiving a trigger frame from the physical access point,
the trigger frame reserving a transmission opportunity on at least
one communication channel of the wireless network, the transmission
opportunity including random resource units that the stations may
access using a contention scheme, the trigger frame identifying the
first group and a second group, stations of which are allowed to
contend for access to the random resources units included in the
transmission opportunity to transmit data;
[0047] obtaining a joint set of random access parameters to be used
in common by stations of the first and second groups to contend for
access to a random resource unit included in the transmission
opportunity; and
[0048] contending for access to the random resource unit using the
obtained joint set of random access parameters.
[0049] Correspondingly, the invention also regards a station device
in a wireless network comprising a physical access point and a
plurality of stations organized into groups, each group being
managed by a virtual access point implemented in the physical
access point, the station, belonging to a first group,
comprising:
[0050] at least one microprocessor configured for carrying out the
following steps:
[0051] receiving a trigger frame from the physical access point,
the trigger frame reserving a transmission opportunity on at least
one communication channel of the wireless network, the transmission
opportunity including random resource units that the stations may
access using a contention scheme, the trigger frame identifying the
first group and a second group, stations of which are allowed to
contend for access to the random resources units included in the
transmission opportunity to transmit data;
[0052] obtaining a joint set of random access parameters to be used
in common by stations of the first and second groups to contend for
access to a random resource unit included in the transmission
opportunity; and
[0053] contending for access to the random resource unit using the
obtained joint set of random access parameters.
[0054] In one implementation, a set of random access parameters
includes a lower boundary OCWmin and/or higher boundary OCWmax,
both defining a selection range from which a size of a contention
window OCW for random access is selected.
[0055] In one implementation, the contention scheme at the station
decrements a backoff value OBO of a backoff counter initially drawn
in the range of the contention window for random access [0, OCW],
and triggers access to a random resource unit in the transmission
opportunity upon the backoff value reaching a target value.
[0056] In one implementation, the joint set of random access
parameters is obtained from the received trigger frame.
[0057] In one implementation, the joint set of random access
parameters is obtained from a beacon frame, separate from the
trigger frame, received from the physical access point.
[0058] In one implementation, a plurality of sets of random access
parameters are received from the physical access point in one or
more beacon frames, each set being associated with one group for
use by the stations of that group to contend for access to random
resources units of a transmission opportunity reserved by a trigger
frame for the stations of the group.
[0059] In one implementation, each set of random access parameters
is sent by the physical access point in a separate beacon frame of
the virtual access point managing the group of stations associated
with the set.
[0060] In one implementation, the joint set of random access
parameters is additional to the plurality of sets and is included
in one of the beacon frames.
[0061] In one implementation, the joint set of random access
parameters is included in the beacon frame received from the
virtual access point managing the first group.
[0062] In one implementation, the joint set of random access
parameters is one of the plurality of sets of random access
parameters.
[0063] In one implementation, at least one beacon frame includes an
indication indicating which one of the plurality of sets is to be
used as the joint set of random access parameters.
[0064] In one implementation, the trigger frame includes an
indication indicating which one of the plurality of sets is to be
used as the joint set of random access parameters.
[0065] In one implementation, each group is uniquely identified by
a specific basic service set identification, BSSID.
[0066] In one implementation, the joint set of random access
parameters is selected among the plurality of sets based on the
BSSID of the associated group.
[0067] In one implementation, the set associated with the group
having the lowest BSSID is selected as the joint set of random
access parameters.
[0068] In one implementation, each BSSID is derived from a base
BSSID specific to the physical access point.
[0069] In one implementation, the set associated with the group
identified by the base BSSID is selected as the joint set of random
access parameters.
[0070] In one implementation, the joint set of random access
parameters is selected among the plurality of sets based on a
predefined rule known to stations of the first and the second
group.
[0071] In one implementation, the set associated with the group of
the virtual access point that sent the trigger frame is selected as
the joint set of random access parameters.
[0072] In one implementation, the method further comprises:
[0073] upon receiving of another trigger frame reserving another
transmission opportunity, the other transmission opportunity
including random resource units that the stations may access using
a contention scheme, the other trigger frame identifying only the
first group, stations of which are allowed to contend for access to
the random resources units included in the other transmission
opportunity to transmit data;
[0074] storing at least one of the obtained set of random
parameters, a current value of a backoff counter and a current
value of the contention window OCW;
[0075] obtaining another set of random access parameters to be used
by the station to contend for access to a random resource unit
included in the other transmission opportunity; and
[0076] contending for access to the random resource unit using the
other obtained set of random access parameters.
[0077] The present invention proposes, according to a third aspect,
a wireless communication method in a wireless network comprising a
physical access point and a plurality of stations organized into
groups, each group being managed by a virtual access point
implemented in the physical access point, the method comprising the
following steps, at one station belonging to a first group:
[0078] receiving a first trigger frame from the physical access
point, the first trigger frame reserving a first transmission
opportunity on at least one communication channel of the wireless
network, the first transmission opportunity including random
resource units that the stations may access using a contention
scheme, the first trigger frame identifying only the first group,
stations of which are allowed to contend for access to the random
resources units included in the first transmission opportunity to
transmit data;
[0079] obtaining a first set of random access parameters to be used
by the station to contend for access to a random resource unit
included in the first transmission opportunity;
[0080] contending for access to the random resource unit using the
obtained first set of random access parameters; and
[0081] upon receiving of a second trigger frame reserving a second
transmission opportunity, the second transmission opportunity
including random resource units that the stations may access using
a contention scheme, the second trigger frame identifying the first
group and a second group, stations of which are allowed to contend
for access to the random resources units included in the second
transmission opportunity to transmit data:
[0082] storing at least one of the first set of random parameters,
a current value of a backoff counter and a current value of a
contention window;
[0083] obtaining a second set of random access parameters to be
used by the station to contend for access to a random resource unit
included in the second transmission opportunity; and
[0084] contending for access to the random resource unit using the
obtained second set of random access parameters.
[0085] Correspondingly, the invention also regards a station device
in a wireless network comprising a physical access point and a
plurality of stations organized into groups, each group being
managed by a virtual access point implemented in the physical
access point, the station, belonging to a first group,
comprising:
[0086] at least one microprocessor configured for carrying out the
following steps:
[0087] receiving a first trigger frame from the physical access
point, the first trigger frame reserving a first transmission
opportunity on at least one communication channel of the wireless
network, the first transmission opportunity including random
resource units that the stations may access using a contention
scheme, the first trigger frame identifying only the first group,
stations of which are allowed to contend for access to the random
resources units included in the first transmission opportunity to
transmit data;
[0088] obtaining a first set of random access parameters to be used
by the station to contend for access to a random resource unit
included in the first transmission opportunity;
[0089] contending for access to the random resource unit using the
obtained first set of random access parameters; and
[0090] upon receiving of a second trigger frame reserving a second
transmission opportunity, the second transmission opportunity
including random resource units that the stations may access using
a contention scheme, the second trigger frame identifying the first
group and a second group, stations of which are allowed to contend
for access to the random resources units included in the second
transmission opportunity to transmit data:
[0091] storing at least one of the first set of random parameters,
a current value of a backoff counter and a current value of a
contention window;
[0092] obtaining a second set of random access parameters to be
used by the station to contend for access to a random resource unit
included in the second transmission opportunity; and
[0093] contending for access to the random resource unit using the
obtained second set of random access parameters.
[0094] In one implementation, the method further comprises:
[0095] upon receiving of a third trigger frame reserving a third
transmission opportunity, the third transmission opportunity
including random resource units that the stations may access using
a contention scheme, the third trigger frame identifying only the
first group, stations of which are allowed to contend for access to
the random resources units included in the third transmission
opportunity to transmit data;
[0096] restoring at least one of the first set of random
parameters, a current value of a backoff counter and a current
value of the contention window; and
[0097] contending for access to the random resource unit using the
restored parameters and/or values.
BRIEF DESCRIPTION OF THE DRAWINGS
[0098] Further advantages of the present invention will become
apparent to those skilled in the art upon examination of the
drawings and detailed description. Embodiments of the invention
will now be described, by way of example only, and with reference
to the following drawings.
[0099] FIG. 1 illustrates a typical wireless communication system
in which embodiments of the invention may be implemented;
[0100] FIG. 2 illustrates 802.11ac channel allocation that support
channel bandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in
the art;
[0101] FIG. 3 illustrates an example of 802.11ax uplink OFDMA
transmission scheme, wherein the AP issues a Trigger Frame for
reserving a transmission opportunity of OFDMA sub-channels
(resource units) on an 80 MHz channel as known in the art;
[0102] FIGS. 4a, 4b and 4c present the format of a beacon frame
according to the 802.11 standard, including the Information
Elements representative of the RAPS set and the Multi-BSS
configuration;
[0103] FIG. 5 illustrates some exemplary situations of the
aforementioned issues of trigger frames belonging to distinct BSS
contexts.
[0104] FIG. 6 shows a schematic representation a communication
device in accordance with embodiments of the present invention;
[0105] FIG. 7 shows a schematic representation of a wireless
communication device in accordance with embodiments of the present
invention;
[0106] FIG. 8 illustrates an exemplary transmission block of a
communication non-AP station according to embodiments of the
invention;
[0107] FIGS. 9a and 9b illustrate, using a flowchart, general steps
of AP emitting a beacon frame for multiple BSS, according to
embodiments of the invention;
[0108] FIG. 10 illustrates, using a flowchart, general steps of a
non-AP station receiving a Trigger Frame with multiple BSS support,
according to embodiments of the invention; and
[0109] FIGS. 11a and 11b present first general embodiments of the
invention implemented, respectively, at a physical access point and
at a station belonging to a first group of stations.
DETAILED DESCRIPTION
[0110] The invention will now be described by means of specific
non-limiting exemplary embodiments and by reference to the
figures.
[0111] FIG. 1 illustrates a communication system in which several
communication nodes (or stations) 101-107 exchange data frames over
a radio transmission channel 100 of a wireless local area network
(WLAN), under the management of a central station, or access point
(AP) 110. The radio transmission channel 100 is defined by an
operating frequency band constituted by a single channel or a
plurality of channels forming a composite channel.
[0112] Access to the shared radio medium to send data frames is
based on the CSMA/CA technique, for sensing the carrier and
avoiding collision by separating concurrent transmissions in space
and time.
[0113] Carrier sensing in CSMA/CA is performed by both physical and
virtual mechanisms. Virtual carrier sensing is achieved by
transmitting control frames to reserve the medium prior to
transmission of data frames.
[0114] Next, a source or transmitting station, including the AP,
first attempts through the physical mechanism, to sense a medium
that has been idle for at least one DIFS (standing for DCF
InterFrame Spacing) time period, before transmitting data
frames.
[0115] However, if it is sensed that the shared radio medium is
busy during the DIFS period, the source station continues to wait
until the radio medium becomes idle.
[0116] To access the medium, the station starts a countdown backoff
counter designed to expire after a number of timeslots, chosen
randomly in the contention window range [0, CW], CW (integer) being
also referred to as the Contention Window size and defining the
upper boundary of the backoff selection interval (contention window
range). This backoff mechanism or procedure is the basis of the
collision avoidance mechanism that defers the transmission time for
a random interval, thus reducing the probability of collisions on
the shared channel. After the backoff time period, the source
station may send data or control frames if the medium is idle.
[0117] One problem of wireless data communications is that it is
not possible for the source station to listen while sending, thus
preventing the source station from detecting data corruption due to
channel fading or interference or collision phenomena. A source
station remains unaware of the corruption of the data frames sent
and continues to transmit the frames unnecessarily, thus wasting
access time.
[0118] The Collision Avoidance mechanism of CSMA/CA thus provides
positive acknowledgement (ACK) of the sent data frames by the
receiving station if the frames are received with success, to
notify the source station that no corruption of the sent data
frames occurred.
[0119] The ACK is transmitted at the end of reception of the data
frame, immediately after a period of time called Short InterFrame
Space (SIFS).
[0120] If the source station does not receive the ACK within a
specified ACK timeout or detects the transmission of a different
frame on the channel, it may infer data frame loss. In that case,
it generally reschedules the frame transmission according to the
above-mentioned backoff procedure.
[0121] The wireless communication system of FIG. 1 comprises a
physical access point 110 configured to manage two or more WLANs
(or BSSs), i.e. two or more groups of stations. Each BSS is
uniquely identified by a specific basic service set identification,
BSSID and managed by a virtual AP implemented in the physical
AP.
[0122] In the example shown, the physical AP implements two virtual
APs, virtual AP 1 VAP-1 (110A) having MAC address MAC1 as specific
BSSID to manage a first WLAN (BSS), and virtual AP 2 VAP-2 (110B)
having MAC address MAC2 as specific BSSID to manage a second WLAN
(BSS). Of course more WLANs can be implemented, requiring a
corresponding number of virtual APs to be implemented in the
physical AP.
[0123] All MAC addresses for the virtual APs are generated based on
(or "derive from") a base MAC address specific to the physical
access point, usually the base 48-bit MAC address of AP 110. For
instance MAC.sub.i (`i` being a BSS index) used as specific
BSSID(i) for virtual AP.sub.i is generated as follows, from the
base MAC address BASE_BSSID:
[0124] MAC.sub.i=BSSID(i)=(BASE_BSSID modified to set the n LSBs to
zero)|((n LSBs of BASE_BSSID)+i) mod 2 n)
[0125] where LSB refers to the least significant bits, "n" is an AP
parameter (integer) defining the maximum number (about 2.sup.n) of
possible specific BSSIDs, and `I` operator is an XOR operator. The
specific BSSID(i) thus differ one from the other by their n LSBs.
The 48-n MSBs of the generated specific BSSIDs are all similar to
the corresponding bits of BASE_BSSID.
[0126] As an example, virtual AP 1 provides a WLAN with "guest" as
SSID that one or more stations can join, while virtual AP 2
provides a WLAN with "Employee" as SSID that other stations can
join simultaneously. The security for each WLAN is different, i.e.
WEP and WPA. A same device can usually join two WLANs
simultaneously if it has two separate WLAN interfaces (e.g. wifi
network card). In that case, the device is considered as two
stations in the network, each station being able to join only one
WLAN at a time.
[0127] Some control frames sent by the AP are an important part of
802.11, for instance beacon frames and probe response frames. The
stations are waiting for these frames to know about the WLANs or
BSSs available.
[0128] These frames let the stations know that an AP and one or
more WLANs are available, but also notify the stations about
important information such as the corresponding SSID or SSIDs, the
corresponding specific BSSID or BSSIDs, the communication mode
(Infrastructure or Ad-Hoc), the protection security schemes used
(e.g. Open, WEP, WPA-PSK or 802.1X), the support transmission rates
used, the channel in operation and optional Information
Elements.
[0129] When multiple BSSs are provided, multiple beacons are
transmitted by the AP, one for each active BSS, usually each 100
ms. It results in that the stations have to process beacon frames
more frequently and that channel occupation due to control frames
is increased (being noted that the control frames such as the
beacon frames are transmitted at low rate).
[0130] These drawbacks can be reduced by for example increasing the
beacon interval (more than 100 ms) so that the beacon frame of each
BSS is sent less frequently. However, this may cause some stations
not to detect the beacon frame of a given BSS when scanning, and
thus to decide a particular BSS (through its SSID) is not
available.
[0131] To improve this situation, the IEEE 802.11v Wireless Network
Management specification provides a mechanism to advertise multiple
security profiles including BSSID advertisements. Thus, a single
Beacon frame is sent rather than multiple Beacon frames in order to
advertise a plurality of specific BSSIDs/SSIDs. In this mechanism,
a new Information Element (IE) is defined (Multiple BSSID IE) in
the beacon frames sent by one or the other of the multiple virtual
APs (i.e. specific BSSIDs).
[0132] The transmitter address of such a beacon frame includes the
specific BSSID of the transmitting virtual AP. Furthermore, the
Multiple BSSID IE indicates that multiple BSSs is contemplated and
provides an indication of the maximum number of BSSs, parameter
"n", to the stations, as well as the common, inherited information
element values of all of the BSSs (e.g. so that all members of the
set use a common operating class, channel, channel access
functions, etc.) and the unique information elements of each of the
other BSSs indexed by their BSSID indexes `i` (i.e. different
advertised capabilities of the various BSSs, including ones from
the BSS of the transmitting VAP).
[0133] As mentioned above, a BSSID index `i` is a value between 1
and 2.sup.n-1, which identifies the BSSID. It may also be noted
that the AP may include two or more Multiple BSSID elements
containing elements for a given BSSID index in one Beacon
frame.
[0134] Such a multi BSS beacon frame may also transmit the base
address BASE_BSSID to the stations.
[0135] To meet the ever-increasing demand for faster wireless
networks to support bandwidth-intensive applications, 802.11ac is
targeting larger bandwidth transmission through multi-channel
operations. FIG. 2 illustrates 802.11ac channel allocation that
support composite channel bandwidth of 20 MHz, 40 MHz, 80 MHz or
160 MHz.
[0136] IEEE 802.11ac introduces support of a restricted number of
predefined subsets of 20 MHz channels to form the sole predefined
composite channel configurations that are available for reservation
by any 802.11ac station on the wireless network to transmit
data.
[0137] The predefined subsets are shown in the Figure and
correspond to 20 MHz, 40 MHz, 80 MHz, and 160 MHz channel
bandwidths, compared to only 20 MHz and 40 MHz supported by
802.11n. Indeed, the 20 MHz component channels 200-1 to 200-8 are
concatenated to form wider communication composite channels.
[0138] In the 802.11ac standard, the channels of each predefined 40
MHz, 80 MHz or 160 MHz subset are contiguous within the operating
frequency band, i.e. no hole (missing channel) in the composite
channel as ordered in the operating frequency band is allowed.
[0139] The 160 MHz channel bandwidth is composed of two 80 MHz
channels that may or may not be frequency contiguous. The 80 MHz
and 40 MHz channels are respectively composed of two frequency
adjacent or contiguous 40 MHz and 20 MHz channels, respectively.
However the present invention may have embodiments with either
composition of the channel bandwidth, i.e. including only
contiguous channels or formed of non-contiguous channels within the
operating band.
[0140] A station (including the AP) is granted a TxOP through the
enhanced distributed channel access (EDCA) mechanism on the
"primary channel" (200-3). Indeed, for each composite channel
having a bandwidth, 802.11ac designates one channel as "primary"
meaning that it is used for contending for access to the composite
channel. The primary 20 MHz channel is common to all stations
(STAs) belonging to the same basic set, i.e. managed by or
registered to the same local Access Point (AP).
[0141] However, to make sure that no other legacy station (i.e. not
belonging to the same set) uses the secondary channels, it is
provided that the control frames (e.g. RTS frame/CTS frame or
trigger frame described below) reserving the composite channel are
duplicated over each 20 MHz channel of such composite channel.
[0142] As addressed earlier, the IEEE 802.11ac standard enables up
to four, or even eight, 20 MHz channels to be bound. Because of the
limited number of channels (19 in the 5 GHz band in Europe),
channel saturation becomes problematic. Indeed, in densely
populated areas, the 5 GHz band will surely tend to saturate even
with a 20 or 40 MHz bandwidth usage per Wireless-LAN cell.
[0143] Developments in the 802.11ax standard seek to enhance
efficiency and usage of the wireless channel for dense
environments.
[0144] In this perspective, one may consider multi-user (MU)
transmission features, allowing multiple simultaneous transmissions
to different users in both downlink (DL) and uplink (UL)
directions, once a transmission opportunity has been reserved. In
the uplink, multi-user transmissions can be used to mitigate the
collision probability by allowing multiple non-AP stations to
simultaneously transmit to the AP.
[0145] To actually perform such multi-user transmission, it has
been proposed to split a granted 20MHz channel (200-1 to 200-4)
into at least one sub-channel, but preferably a plurality
sub-channels 310 (elementary sub-channels), also referred to as
sub-carriers or resource units (RUs) or "traffic channels", that
are shared in the frequency domain by multiple users, based for
instance on Orthogonal Frequency Division Multiple Access (OFDMA)
technique.
[0146] This is illustrated with reference to FIG. 3.
[0147] The multi-user feature of OFDMA allows the AP to assign
different RUs to different stations in order to increase
competition within a reserved transmission opportunity TXOP. This
may help to reduce contention and collisions inside 802.11
networks.
[0148] In this example, each 20 MHz channel (200-1, 200-2, 200-3 or
200-4) is sub-divided in frequency domain into four OFDMA
sub-channels or RUs 310 of size 5 MHz. Of course the number of RUs
splitting a 20 MHz channel may be different from four. For
instance, between two to nine RUs may be provided (thus each having
a size between 10 MHz and about 2 MHz). It is also possible to have
a RU width greater than 20 MHz, when included inside a wider
composite channel (e.g. 80 MHz).
[0149] Contrary to downlink OFDMA wherein the AP can directly send
multiple data to multiple stations (supported by specific
indications inside the PLOP header), a trigger mechanism has been
adopted for the AP to trigger MU uplink communications from various
non-AP stations.
[0150] To support a MU uplink transmission (during a TXOP
pre-empted by the AP), the 802.11ax AP has to provide signalling
information for both legacy stations (i.e. non-802.11ax stations)
to set their NAV and for 802.11ax client stations to determine the
Resource Units allocation.
[0151] In the following description, the term legacy refers to
non-802.11ax stations, meaning 802.11 stations of previous
technologies that do not support OFDMA communications.
[0152] As shown in the example of FIG. 3, the AP sends a trigger
frame (TF) 330 to the targeted 802.11ax stations to reserve a
transmission opportunity. The bandwidth or width of the targeted
composite channel for the transmission opportunity is signalled in
the TF frame, meaning that the 20, 40, 80 or 160 MHz value is
signalled. The TF frame is a control frame, according the 802.11
legacy non-HT format, and is sent over the primary 20 MHz channel
and duplicated (replicated) on each other 20 MHz channels forming
the targeted composite channel. Due to the duplication of the
control frames, it is expected that every nearby legacy station
(non-HT or 802.11ac stations) receiving the TF on its primary
channel, then sets its NAV to the value specified in the TF frame.
This prevents these legacy stations from accessing the channels of
the targeted composite channel during the TXOP.
[0153] Based on an AP's decision, the trigger frame TF may define a
plurality of resource units (RUs) 310. The multi-user feature of
OFDMA allows the AP to assign different RUs to different client
stations in order to increase competition. This may help to reduce
contention and collisions inside 802.11 networks.
[0154] The trigger frame 330 may designate "Scheduled" RUs, which
may be reserved by the AP for certain stations in which case no
contention for accessing such RUs is needed for these stations.
Such RUs and their corresponding scheduled stations are indicated
in the trigger frame. For instance, a station identifier, such as
the Association ID (AID) assigned to each station upon
registration, is added in association with each Scheduled RU in
order to explicitly indicate the station that is allowed to use
each Scheduled RU. Such transmission mode is concurrent to the
conventional EDCA mechanism.
[0155] The trigger frame TF may also designate "Random" RUs, in
addition or in replacement of the "Scheduled" RUs. The Random RUs
can be randomly accessed by the stations of the BSS. In other
words, Random RUs designated or allocated by the AP in the TF may
serve as basis for contention between stations willing to access
the communication medium for sending data. A collision occurs when
two or more stations attempt to transmit at the same time over the
same RU. An AID equal to 0 may be used to identify random RUs.
[0156] A random allocation procedure may be considered for 802.11ax
standard based on an additional backoff counter (OFDMA backoff
counter, or OBO counter or RU counter, as further illustrated as
800 in FIG. 8) for RU contention by the 802.11ax non-AP stations,
i.e. to allow them for performing contention between them to access
and send data over a Random RU. The RU backoff counter is distinct
from the EDCA backoff counters (as illustrated as 811 in FIG. 8).
However data transmitted in an accessed OFDMA RUs 310 is assumed to
be served from same EDCA traffic queues (as illustrated as 810 in
FIG. 8).
[0157] The RU random allocation procedure comprises, for a station
of a plurality of 802.11ax stations having an positive RU backoff
value (initially drawn inside an RU contention window range), a
first step of determining, from a received trigger frame, the
sub-channels or RUs of the communication medium available for
contention (the so-called "random RUs"), a second step of verifying
if the value of the RU backoff value local to the considered
station is not greater than the number of detected-as-available
random RUs, and then, in case of successful verification, a third
step of randomly selecting a RU among the detected-as-available RUs
to then send data. In case the second step is not verified, a
fourth step (instead of the third) is performed in order to
decrement the RU backoff counter by the number of
detected-as-available random RUs.
[0158] The metrics or parameters of the OFDMA-based RU random
access mechanism (such as the RU contention window range, used to
draw the RU backoff) are signaled by an AP through beacon frames in
a new Information Element, called the RAPS element (RAPS stands for
OFDMA-based Random Access Parameter Set). The format of the RAPS
element is further defined in FIG. 4c. A non-AP station uses the
RAPS element provided by the AP to which the station is associated.
The RAPS is introduced with respect to a single BSS group of
stations that is managed by one access point with which each
station has previously registered.
[0159] As one can note, a station is not guaranteed to perform
OFDMA transmission over a random RU for each TF received. This is
because at least the RU backoff counter is decremented upon each
reception of a Trigger Frame by the number of proposed Random RUs,
thereby differing data transmission to a subsequent trigger frame
(depending of the current value of the RU backoff number and of the
number of random RUs offered by each of further received TFs).
[0160] Back to FIG. 3, it results from the various possible
accesses to the RUs that some of them are not used (310u) because
no station with an RU backoff value less than the number of
available random RUs has randomly selected one of these random RUs,
whereas some other RUs have collided (as example 310c) because at
least two of these stations have randomly selected the same random
RU. This shows that due to the random determination of random RUs
to access, collision may occur over some RUs, while other RUs may
remain free.
[0161] Once the stations have used the Scheduled and/or Random RUs
to transmit data to the AP, the AP responds with a Multi-User
acknowledgment (not show in the Figure) to acknowledge the data on
each RU.
[0162] The MU Uplink (UL) medium access scheme, including both
scheduled RUs and random RUs, proves to be very efficient compared
to conventional EDCA access scheme, especially in dense
environments as envisaged by the 802.11ax standard. This is because
the number of collisions generated by simultaneous medium access
attempts and the overhead due to the medium access are both
reduced.
[0163] As a result, the usage of Trigger Frame is naturally
extended to cover multiple BSS. The Trigger frame is directed to
stations that the AP intends to communicate with at least two
different BSSs.
[0164] In addition, non-associated stations (that is to say non-AP
stations not yet associated to an AP) can use the RU random access
procedure in order to be allowed to transmit towards the AP in any
randomly allocated resource unit. Aim is to support easy
association procedure in dense environments.
[0165] As currently designed, the RU random access mechanism
(including the RAPS settings and the RU backoff management) is
specific to a single BSS, meaning that only the stations belonging
to a specific BSS are provided guidance to access the resource
units included in the transmission opportunity reserved by the
trigger frame emitted for such BSS. For instance, some exemplary
issues will be further provided in regards to FIG. 5.
[0166] FIG. 4a represents an example format of a beacon frame
usable in a 802.11 type WLAN. The represented format is given for
illustrative purposes and other formats may be used. The beacon
frame is a management frame used by access points in an
infrastructure BSS to communicate throughout the serviced area the
characteristics of the connection offered to the BSS members.
Information provided in the beacon frame may be used by client
stations for joining the network as well as client stations already
associated with the BSS. Note that the beacon frame can also be
used by stations in an independent BSS (IBSS), i.e. an ad hoc
network that contains no access points. As example, some stations
may act as a soft-AP (software implemented), that is to say
implementing all the functionalities of an IEEE 802.11 Access Point
but in an adhoc or transient connection mode typically for a
specific purpose (for illustration, for example sharing documents
during a meeting or playing multiple-player computer games).
[0167] Illustrated beacon frame 430 contains 24 octets of MAC
header (fields 401 to 406), 0 to 2312 octets of Frame Body 407, and
4 octets of Frame Check Sequence (FCS) 408. The MAC header includes
the following fields: a frame control field 401 (to indicate that
the frame is a management frame of beacon subtype), a duration
field 402 (set to zero), a RA (Receiver or Destination Address)
field 403 (set to broadcast value FF:FF:FF:FF:FF:FF), a TA
(Transmitter or Source Address) field 404 and a BSSID field 405.
The BSSID field contains the identification (ID) of the BSS, which
is the MAC address of the access point servicing the BSS, i.e.
identical to the content of the TA field. The Frame Body is a field
of variable length and consists of two sets of fields: 1) fields
that are mandatory 410, followed by 2) optional fields in the form
of Information Elements (IEs) 411.
[0168] Mandatory information in field 410 may contain: a Timestamp
representing the time at the access point, which is the number of
microseconds the AP has been active, and allowing synchronization
between non-AP stations in a BSS; Beacon Interval representing the
number of time units (TUs) between successive target beacon
transmission times (TBTTs); and capability Info to indicate
requested or advertised optional capabilities and Supported Rates
fields.
[0169] All Information Elements in field 411 share a common general
format consisting of 1 octet Element ID field, a 1 octet Length
field, an optional 1 octet Element ID Extension field, and a
variable-length element-specific Information field. Each
information element is identified by the contents of the Element ID
and, when present, Element ID Extension fields as defined in the
802.11 standard. The Length field specifies the number of octets
following the Length field.
[0170] It is possible to address stations of a plurality of BSSs
with a single beacon frame transmitted by one of the virtual APs of
the physical AP, rather than multiple beacon frames transmitted by
multiple virtual APs. The virtual AP transmitting the beacon frame
(thus having its MAC address in the TA 404 and BSSID 405 fields) is
referred to as representative AP or transmitted BSSID. The other
virtual APs of the physical AP are referred to as represented APs
or non-transmitted BSSIDs, as their addresses do not appear in the
TA 404 and BSSID 405 fields of the beacon frame.
[0171] A Multiple BSSID information element is defined in the
single beacon frame to carry the common, inherited information
element values of all of the BSSIDs and the unique information
elements of the non-transmitted BSSIDs (represented virtual APs).
The BSSIDs of the represented virtual APs can thus be derived from
the Multiple BSSID information element.
[0172] FIG. 4b represents an example format of a Multiple BSSID
element.
[0173] The multiple BSSID information element, referenced 411a,
comprises a 1-byte MAX BSSID indicator field 420 and a variable
length Optional Sub-elements field 421.
[0174] More than one Multiple BSSID element may be included in a
beacon frame. The MAX BSSID Indicator field is `n`, where 2.sup.n
is the maximum number of BSSIDs supported by the access point,
including the transmitted BSSID.
[0175] Optional Sub-elements field 421 contains zero or more
sub-elements in its Data field, such as for example the
"non-transmitted BSSID profile" sub-element.
[0176] The "non-transmitted BSSID Profile" is identified by a
Sub-element ID of value 0, and shall include the SSID and multiple
BSSID-index sub-elements for each of the supported BSSIDs. It may
include the Capabilities field followed by a variable number of
information elements.
[0177] The AP may include two or more Multiple BSSID elements
containing elements for a given BSSID index in one beacon
frame.
[0178] When a station receives a beacon frame with a Multiple BSSID
element that consists of a non-transmitted BSSID profile with only
the mandatory elements (Capability element, SSID and multiple
BSSID-index), it may inherit the complete profile from a previously
received beacon frame.
[0179] FIG. 4c represents an example format of a RAPS Information
Element.
[0180] RAPS (OFDMA-based Random Access Parameter Set) element is
used by (non-AP) stations to configure their UL MU random access
mechanism. The Element_ID, and optionally the Element ID Extension,
identify the RAPS format. A typical parameter that may be included
in the RAPS information element is the range of OFDMA contention
window 441 (OCW Range) for 802.11ax stations willing to initiate
random access following reception of a
[0181] Trigger frame for random access (TF-R). Such a random access
trigger frame is a trigger frame having at least one Random access
RU, that is to say at least one RU associated with no station (the
AID subfield of the User Info field for the RU set to 0). As a
result, non-associated STAs can also transmit on such random RU
because they have no AID.
[0182] The OCW Range field 441 may include subfields EOCWmin and
EOCWmax holding parameters to calculate the minimum (OCWmin) and
the maximum (OCWmax) values of the OCW (OFDMA contention window),
e.g. as follows: [0183] OCWmin=2.sup.EOCWmin-1; and [0184]
OCWmax=2.sup.EOCWmax-1.
[0185] OCWmin represents the minimum value of OCW for the initial
UL transmission using UL OFDMA-based random access to be used by a
station for initial or successful transmission. OCWmax represents
the maximum value of OCW for UL OFDMA-based random access used by a
station for its retransmission attempts of UL OFDMA-based random
access.
[0186] An AP includes the RAPS element in Beacon and Probe Response
frames it transmits.
[0187] FIG. 5 illustrates an exemplary situation in which
embodiments of the invention can be implemented.
[0188] For the sake of illustration, the Trigger Frames considered
in the following are all Trigger Frames offering at least one
random RU.
[0189] In the approach of FIG. 5, the wireless network comprising a
physical access point 110 and a plurality of stations organized
into groups, each group being managed by a virtual access point
(e.g. VAP-1 110A and VAP-2 110B as illustrated in FIG. 1)
implemented in the physical access point. The AP has emitted a
beacon 430 repetitively, containing parameters of each individual
BSS group.
[0190] The stations contend for an access to the wireless network,
and the contention process at each station starts or restarts once
the wireless network is detected as idle for a predefined time
period (usually DIFS time period after the end of a previous TXOP,
for instance after an acknowledgment from the AP or after end of
PPDU transmission).
[0191] The physical access point thus performs the step of sending
a plurality of trigger frames 330-1, 330-2, 330-3 on the wireless
network to reserve successive transmission opportunities on at
least one communication channel of the wireless network, each
transmission opportunity being reserved for a specific group of
stations (BSS) and including resource units that form the
communication channel and that the stations of the specific group
access to transmit data.
[0192] Consequently, the physical access point receives, in
response to each trigger frame and during the corresponding
reserved transmission opportunity, data 310 from one or more
stations of the group specific to the trigger frame.
[0193] The AP thus performs several TXOP reservations according to
the number of BSSs it wants to poll. Each reserved TXOP is
independent from one another, in particular because the stations
not addressed by the trigger frame set their NAV to the Duration
Field specified in the Trigger Frame 330, and thus waits for this
duration.
[0194] As example, the AP acts as a VAP-1 to emit a first TF 330-1,
aiming at triggering stations of BSS-1 group. Secondly, it acts as
VAP-2 to emit a TF 330-2, aiming at triggering stations of BSS-2
group. At any moment, the AP may emit a Trigger Frame for multiple
BSS groups (TF 330-3), aiming at triggering stations of whole BSS
groups managed by the AP. As a result of detecting TF 330-3, a
station will contend for access to the random RUs using parameters
(RAPS) chosen according to embodiments of the invention.
[0195] Random access parameters defined according to embodiments of
the invention may also be used by non-associated (i.e.
non-registered) stations, i.e. not yet belonging to a specific BSS
group, when trying to contend for access to a random RU advertised
by the trigger frame. In fact, these non-associated stations may
try to access because they are not addressed by the trigger frames
and their NAV is not set.
[0196] The present invention seeks to provide a more efficient
usage of the UL MU random access procedure in case of multiple BSS
groups.
[0197] The inventors have contemplated considering the multi-BSSID
group as a distinct BSS group, in particular regarding the
parameters of the UL MU random access procedure. To do so, they
propose allowing the AP to disclose a RAPS profile (also referred
to as context) for the multiple-BSSID case, to be used by non-AP
stations (even the non-associated stations) when triggered for
uplink communication by a Trigger Frame addressed to a multi-BSS
group.
[0198] Various embodiments are proposed below that all relate to a
wireless communication methods and related devices.
[0199] FIG. 11a presents first general embodiments of the invention
implemented at a physical access point.
[0200] At step 1100, a trigger frame is sent by the AP for
reserving a transmission opportunity on at least one communication
channel of the wireless network. The transmission opportunity
including random resource units that the stations may access using
a contention scheme. The trigger frame identifying a plurality of
groups (referred to as multi-BSS trigger frame), stations of which
are allowed to contend for access to the random resources units
included in the transmission opportunity to transmit data.
[0201] At step 1101, AP sends a joint set of random access
parameters (RAPS) to be used in common by stations of the plurality
of groups identified in the trigger frame to contend for access to
a random resource unit included in the transmission opportunity.
The joint set of parameters may be transmitted by the physical AP
according to different variants, among which: transmission in a
beacon frame either as a dedicated information element (Multiple
BSSID element) or a RAPS element containing the parameters for the
transmitted BSSID.
[0202] At step 1102, and in response to the trigger frame,
receiving, over the random resource unit, data from a station of
one of the plurality of identified groups identified in the trigger
frame.
[0203] FIG. 11b presents first general embodiments of the invention
implemented at a station belonging to a first group of
stations.
[0204] At step 1110, a trigger frame is received from the physical
access point. The trigger frame reserving a transmission
opportunity on at least one communication channel of the wireless
network, the transmission opportunity including random resource
units that the stations may access using a contention scheme. The
trigger frame is of type multi-BSS identifying the first group and
a second group, stations of which are allowed to contend for access
to the random resources units included in the transmission
opportunity to transmit data.
[0205] At step 1111, a joint set of random access parameters is
obtained to be used in common by stations of the first and second
groups to contend for access to a random resource unit included in
the transmission opportunity. Different variants may be envisaged
for obtaining the joint set of random access parameters, among
which: [0206] the joint set of random access parameters is obtained
from the received trigger frame. [0207] the joint set of random
access parameters is obtained from a beacon frame, separate from
the trigger frame, received from the physical access point.
[0208] At step 1112, the station contends for access to the random
resource unit using the obtained joint set of random access
parameters.
[0209] FIG. 6 schematically illustrates a communication device 600,
either a non-AP station 101-107 or the access point 110, of the
radio network 100, configured to implement at least one embodiment
of the present invention. The communication device 600 may
preferably be a device such as a micro-computer, a workstation or a
light portable device. The communication device 600 comprises a
communication bus 613 to which there are preferably connected:
[0210] a central processing unit 611, such as a microprocessor,
denoted CPU; [0211] a read only memory 607, denoted ROM, for
storing computer programs for implementing the invention; [0212] a
random access memory 612, denoted RAM, for storing the executable
code of methods according to embodiments of the invention as well
as the registers adapted to record variables and parameters
necessary for implementing methods according to embodiments of the
invention; and [0213] at least one communication interface 602
connected to the radio communication network 100 over which digital
data packets or frames or control frames are transmitted, for
example a wireless communication network according to the 802.11ax
protocol. The frames are written from a FIFO sending memory in RAM
612 to the network interface for transmission or are read from the
network interface for reception and writing into a FIFO receiving
memory in RAM 612 under the control of a software application
running in the CPU 611.
[0214] Optionally, the communication device 600 may also include
the following components: [0215] a data storage means 604 such as a
hard disk, for storing computer programs for implementing methods
according to one or more embodiments of the invention; [0216] a
disk drive 605 for a disk 606, the disk drive being adapted to read
data from the disk 606 or to write data onto said disk; [0217] a
screen 609 for displaying decoded data and/or serving as a
graphical interface with the user, by means of a keyboard 610 or
any other pointing means.
[0218] The communication device 600 may be optionally connected to
various peripherals, such as for example a digital camera 608, each
being connected to an input/output card (not shown) so as to supply
data to the communication device 600.
[0219] Preferably the communication bus provides communication and
interoperability between the various elements included in the
communication device 600 or connected to it. The representation of
the bus is not limiting and in particular the central processing
unit is operable to communicate instructions to any element of the
communication device 600 directly or by means of another element of
the communication device 600.
[0220] The disk 606 may optionally be replaced by any information
medium such as for example a compact disk (CD-ROM), rewritable or
not, a ZIP disk, a USB key or a memory card and, in general terms,
by an information storage means that can be read by a microcomputer
or by a microprocessor, integrated or not into the apparatus,
possibly removable and adapted to store one or more programs whose
execution enables a method according to the invention to be
implemented.
[0221] The executable code may optionally be stored either in read
only memory 607, on the hard disk 604 or on a removable digital
medium such as for example a disk 606 as described previously.
According to an optional variant, the executable code of the
programs can be received by means of the communication network 603,
via the interface 602, in order to be stored in one of the storage
means of the communication device 600, such as the hard disk 604,
before being executed.
[0222] The central processing unit 611 is preferably adapted to
control and direct the execution of the instructions or portions of
software code of the program or programs according to the
invention, which instructions are stored in one of the
aforementioned storage means. On powering up, the program or
programs that are stored in a non-volatile memory, for example on
the hard disk 604 or in the read only memory 607, are transferred
into the random access memory 612, which then contains the
executable code of the program or programs, as well as registers
for storing the variables and parameters necessary for implementing
the invention.
[0223] In a preferred embodiment, the apparatus is a programmable
apparatus which uses software to implement the invention. However,
alternatively, the present invention may be implemented in hardware
(for example, in the form of an Application Specific Integrated
Circuit or ASIC).
[0224] FIG. 7 is a block diagram schematically illustrating the
architecture of the communication device 600, either the AP 110 or
one of stations 101-107, adapted to carry out, at least partially,
the invention. As illustrated, device 600 comprises a physical
(PHY) layer block 703, a MAC layer block 702, and an application
layer block 701.
[0225] The PHY layer block 703 (here an 802.11 standardized PHY
layer) has the task of formatting, modulating on or demodulating
from any 20 MHz channel or the composite channel, and thus sending
or receiving frames over the radio medium used 100, such as 802.11
frames, for instance medium access trigger frames TF 330 (FIG. 3)
to reserve a transmission slot, MAC data and management frames
based on a 20 MHz width to interact with legacy 802.11 stations, as
well as of MAC data frames of OFDMA type having smaller width than
20 MHz legacy (typically 2 or 5 MHz) to/from that radio medium.
[0226] The MAC layer block or controller 702 preferably comprises a
MAC 802.11 layer 704 implementing conventional 802.11ax MAC
operations, and additional blocks 705 and 706 for carrying out, at
least partially, the invention. The MAC layer block 702 may
optionally be implemented in software, which software is loaded
into RAM 612 and executed by CPU 611.
[0227] Preferably, the additional block 705, referred to as
multiple BSS management module for controlling access to random
OFDMA resource units (sub-channels) in case of multiple BSSs,
implements the part of embodiments of the invention that regards
non-AP station and/or AP operations of device 600.
[0228] For instance and not exhaustively, the operations for the AP
may include generating and sending beacon frames as defined below,
i.e. beacon frames identifying a plurality of groups, instead of a
single BSS, including a specific group referencing several BSSs
(multiple-BSS group) forming the whole network cell, and then
managing the RAPS profile for random access of resource units
during the reserved TXOP to such multiple-BSS group; the operations
for a station different from the AP may include analyzing received
beacon frames to determine if the station is allowed to access some
resource units in the context the trigger frames allow several BSSs
to communicate during the reserved TXOP.
[0229] Preferably, the additional block 706, referred as to OFDMA
Medium Access module for configuring and updating the OFDMA-based
UL MU random access procedure, implements the part of embodiments
of the invention that regards non-AP station operations of device
600.
[0230] MAC 802.11 layer 704, multiple BSS management module 705 and
OFDMA Medium Access module 706 interact one with the other in order
to process accurately communications over multiple BSS groups
according to embodiments of the invention.
[0231] On top of the Figure, application layer block 701 runs an
application that generates and receives data packets, for example
data packets of a video stream. Application layer block 701
represents all the stack layers above MAC layer according to ISO
standardization.
[0232] Embodiments of the present invention are now illustrated
using various exemplary embodiments in the context of IEEE 802.11ax
by considering OFDMA sub-channels and multiple BSS groups. Although
the proposed examples use the trigger frame 330 (see FIG. 3) sent
by an AP for a multi-user uplink transmissions, equivalent
mechanisms can be used in a centralized or in an adhoc environment
(i.e. without an AP).
[0233] Although the present invention is also described with
reference to beacon frame embodiments, the present invention is not
limited to beacon frame modification but also any 802.11 management
frame such as the probe response frames.
[0234] Also the invention is not limited to the 802.11ax
context.
[0235] Below, the term legacy refers to non-802.11ax stations,
meaning 802.11 stations of previous technologies that do not
support OFDMA communications.
[0236] FIG. 8 illustrates an exemplary transmission block of a
communication non-AP station 600 according to embodiments of the
invention.
[0237] As mentioned above, the station includes a EDCA channel
access module and possibly an OFDMA access module 706, both
implemented in the MAC layer block 702. The EDCA channel access
module includes: [0238] a plurality of traffic queues 810 for
serving data traffic at different priorities; Usually, four Access
Categories (ACs) are the following in decreasing priority order:
voice (or "AC_VO"), video (or "AC_VI"), best effort (or "AC_BE")
and background (or "AC_BG"). [0239] a plurality of queue backoff
engines 811, each associated with a respective traffic queue for
using a set of EDCA parameters, in particular to compute a
respective queue backoff value, to be used by an associated backoff
counter to contend for access to at least one communication channel
in order to transmit data stored in the respective traffic queue.
[0240] Since the traffic queues or ACs operate concurrently in
accessing the wireless medium, it may happen that two traffic
queues of the same communication station have their backoff ending
simultaneously. In such a situation, a virtual collision handler
(812) of the MAC controller operates a selection of the AC having
the highest priority between the conflicting ACs, and gives up
transmission of data frames from the ACs having lower
priorities.
[0241] Service differentiation between the ACs is achieved by
setting different queue backoff parameters between the ACs, such as
different CW.sub.min, CW.sub.max, AIFSN and/or different
transmission opportunity duration limits (TXOP_Limit). This
contributes to adjusting QoS. This is the EDCA access scheme.
[0242] The OFDMA access module includes an OBO backoff engine 800
separate from the queue backoff engines, for using RU contention
parameters, in particular to compute an RU backoff value, to be
used by an RU backoff counter to contend for access to the OFDMA
random resource units defined in a received TF (sent by the AP for
instance), in order to transmit data stored in either traffic queue
in an OFDMA RU. The OBO backoff engine 800 is associated with a
transmission module, referred to as OFDMA muxer 801. For example
OFDMA muxer 801 is in charge, when the RU backoff value described
below reaches zero, of selecting data to be sent from the AC queues
810.
[0243] The conventional AC queue back-off registers 811 drive the
medium access request along EDCA protocol (channel contention
access scheme), while in parallel, the OBO backoff engine 800
drives the medium access request onto OFDMA multi-user protocol (MU
UL contention access scheme).
[0244] As these two contention access schemes coexist, the non-AP
station implements a medium access mechanism with collision
avoidance based on a computation of backoff values: [0245] a queue
backoff counter value corresponding to a number of time-slots the
station waits (in addition to an AIFS period), after the
communication medium has been detected to be idle, before accessing
the medium. This is EDCA; [0246] an RU backoff counter value
corresponding to a number of idle random RUs the station detects,
after a TXOP has been granted to the AP or any other station over a
composite channel formed of RUs, before accessing the medium.
[0247] The multiple BSS management module 705 aims at storing RAPS
profiles for at least two BSS groups, and supports the
configuration of OBO backoff engine 800 for controlling access to
random OFDMA resource units (sub-channels) for a given BSS group.
This procedure will be further detailed according description of
FIG. 10.
[0248] FIGS. 9a and 9b illustrates, through flowcharts, two
embodiments in which the AP provides RAPS profiles for non-AP
stations of various BSSs. Similar steps have same references.
[0249] These methods are typically implemented in an access point
of the invention.
[0250] Initially, a list of RAPS profiles (each for a given BSS) is
generated in addition to classical (e.g. security) profiles and
SSIDs to be advertised (step 900).
[0251] The profiles of transmitted BSSID group are provided in list
of IE 411 of the beacon frame body 407. The profiles of at least
one non-transmitted BSSID group are provided through Multiple BSSID
elements 411a to be appended later in list 411 of the beacon frame
body 407.
[0252] In case of only one BSS is supported by the AP ("No" to test
902), the algorithm continues to step 905 comprising formatting the
beacon frame and later periodically emitting that beacon frame
(step 906).
[0253] If multi-BSS support is required ("yes" to test 902), a
dedicated RAPS profile corresponding to the plurality of groups of
stations is added to the Beacon Frame (steps 903 and 904).
[0254] This dedicated RAPS profile or element (further identified
as MBSS-RAPS) aims to be used by any station for contending access
during a TXOP reserved for a plurality of groups of stations (e.g.
by means of Trigger Frame 330-3 of FIG. 4) to upload data to
AP.
[0255] The OCW Range (441) for the MBSS-RAPS may be adapted to the
whole cell; for example by averaging various EOCWmin and EOCWmax
values used for the different BSS groups. The AP may use any
proprietary or internal consideration for determining these values,
as for example the density of stations, measured contention or
network load encountered in each individual BSS it manages.
[0256] Preferably, the MBSS-RAPS (which format is compliant with
411b) is directly provided as an Information Element in the list
411: for that purpose, values of Element_ID and Element_ID
Extension fields are used to guarantee that the MBSS-RAPS element
be distinct from RAPS elements already defined for individual
BSSs.
[0257] Alternatively, the MBSS-RAPS is defined through a distinct
Multiple BSSID element 411a, identifying that the concerned BSS is
a multiple BSS. This new multiple BSSID information element would
comprise the same MAX BSSID indicator value, but the MBSS-RAPS is
conveyed inside a newly defined Non-Transmitted BSSID Profile
corresponding to all (or at least several) BSSs. This
Non-Transmitted BSSID Profile for MBSS-RAPS transmission can be
identified by a Sub-element ID of value distinct from 0.
[0258] As a result, the AP has managed transmission to the non-AP
stations of an additional RAPS profile, called the MBSS-RAPS
profile, dedicated to the multi-BSS Trigger Frame case.
[0259] Alternative method of FIG. 9b consists in a distinct manner
to provide the MBSS-RAPS profile compared to the previous method of
FIG. 9a.
[0260] In order to limit the number of RAPS elements provided into
the beacon frame, the basic profile of the transmitted BSSID, i.e.
of the representative AP, is selected as MBSS-RAPS profile, i.e.
joint profile for the BSSs (step 914). That is to say the RAPS
profile to be used by non-AP stations will be the RAPS profile of
the transmitted BSSID, that is the BSS identified by BSSID field
405. As a result, the RAPS profile (embedding the MBSS-RAPS values)
is located in the list 411, before any Multiple BSSID element 411a
of non-transmitted BSSIDs. Access to this profile requires less
processing and is quicker.
[0261] Optionally, the computation of values forming the OCW Range
may be different from previous scheme as the parameters are
identical for Trigger Frames received in a single transmitted BSS
and multi-BSS contexts (step 913).
[0262] The approach of FIG. 9b saves bandwidth space in management
frames such as the beacon frames.
[0263] Thus, a rule is proposed as a variant for associated
stations: when a station is associated with a BSS with a
non-transmitted BSSID, the station selects the RAPS from the
transmitted BSSID Beacon frame for responding to any further
reception of a multiple BSS Trigger frame. As a result, associated
stations manage at most two RAPS contexts (for their own BSS, and
for the multi-BSS context represented by the transmitted
BSSID).
[0264] This has also a great advantage for non-associated stations:
when a station is not yet associated to a BSS, it has only to store
and use the RAPS from the transmitted BSSID Beacon frame when it
receives a multiple BSS Trigger frame.
[0265] Alternative method of FIG. 9b provides further advantages of
using the RAPS profile from the transmitted BSSID as a default
profile: consequently, low-end AP devices may, by simplicity, only
consider this profile for Trigger Frames issued both from their
non-transmitted BSSID contexts (with condition that no specific
RAPS is provided in their non-transmitted BSSID) and for their
multi-BSS context. Those AP devices are considered as low-end
devices because they are limited in their RAPS capabilities to
adapt per BSS to changing conditions (like number of registered
stations, contention, etc.).
[0266] Finally, the Beacon Frame is modified by the AP to identify
a plurality of RAPS profiles allowed to be used for performing
uplink OFDMA transmission in random RUs.
[0267] Any non-AP station that wants to know which RAPS profile it
can access thus has to:
[0268] 1) read, within the received beacon frame, a plurality of
per-BSS RAPS parameter sections 411b additional to legacy
information elements (inside 421); this includes transmitted and
non-transmitted BSSID groups;
[0269] 2) for at least one per-BSS parameter section 420 defining a
BSSID: [0270] determine, based on one BSSID field included in the
per-BSS parameter section (405 or inside 411a), whether it is
willing to join this BSS group, [0271] store, based on the BSSID,
the RAPS profile (along with current OBO and OCW value if any)
inside its module 705.
[0272] Next, as further described by FIG. 10, in case the station
is authorized to access the one or more determined random resource
units for a received Trigger Frame, it accesses at least one of the
determining RAPS profile to initiate the random access procedure
applicable to the reserved transmission opportunity.
[0273] FIG. 10 illustrates, using a flowchart, general steps of a
method according to embodiments of the invention at one station 600
different from the AP. This embodiment can operate with at least
either embodiment of FIG. 9a or embodiment of FIG. 9b at the AP
side.
[0274] At step 1000, station 600 receives a Trigger frame from an
Access Point.
[0275] If the receiving station belongs to a BSS (or virtual BSS)
of the transmitting AP, the Trigger Frame is not filtered by the
PHY layer as defined in the standard. The filtering is made on
so-called "colors" defined in the 802.11ax standard, which mandates
that the BSS colors of all the multiple BSSs managed by a single AP
are the same.
[0276] At step 1001, station 600 analyzes the received trigger
frame at the MAC layer. In particular, TA and RA fields are
analyzed.
[0277] It checks whether the received TF defines a multiple BSS
scheme, with which it is registered (or willing to register
with).
[0278] It consists in checking whether one of TA or RA defines a
plurality of BSSs, e.g. a set of BSSIDs, or not, i.e. if it
includes BASE_BSSID or any other multi-BSS address like the
transmitted BSSID.
[0279] If no multiple BSS scheme is used or the multi-BSS address
does not encompass the specific BSSID of station 600 (e.g. does not
match BASE_BSSID to which station 600 is registered), step 1006 is
implemented by the station consisting in loading from storage of
module 705 the conventional RAPS profile associated with the BSSID
that the station 600 is associated with.
[0280] Otherwise, step 1002 is performed to load the multi-BSS
profile (MBSS-RAPS).
[0281] Alternatively to test 1001, a non-associated station may use
the MBSS-RAPS element for any of the received Trigger Frame(s)
belonging to the same physical AP: that is to say any TF (as
example 330-1/330-2 according to FIG. 5) issued from a VAP will not
conduct to run step 1006, but in contrary to run the step 1002.
This approach has the advantage of only storing one single RAPS
(which is the MBSS-RAPS) by non-associated stations. With regards
to embodiment of FIG. 9b, this single MBSS-RAPS is conveyed through
transmitted BSSID. Until the station is associated, step 1002 is
executed.
[0282] It is to be noted that if the correct context is already
used, step 1002 has no action to perform.
[0283] Then step 1003 is executed within the determined (selected)
RAPS context.
[0284] As noted above, the random RUs can be determined using for
instance the AID associated with each RU defined in the TF (AID=0
may mean random RU). So the number of random Resource Units
supporting the random OFDMA contention scheme (Nb.sub.RU) is known
at this stage. Obtaining the number of random RUs may be
advantageously performed if the number of random RUs varies from
one TF to the other.
[0285] Next, station 600 will decrement the RU backoff value OBO
based on the number Nb.sub.RU of random resource units defined in
the received trigger frame: OBO=OBO-Nb.sub.RU. This is because
station 600 is determined as being an eligible station to transmit
data in an OFDMA random RU, if its pending RU backoff value OBO is
not greater than the number of OFDMA random RUs. This condition
makes the OBO considered as expired.
[0286] In case of no eligibility, the process ends.
[0287] Otherwise, step 1004 is executed to determine the RU the
station can access through contention. It is a RU randomly selected
from the available random RUs (Nb.sub.RU) of the received TF.
[0288] Next to step 1004, step 1005 is performed during which
station 600 accesses the RUs determined at step 1004 and transmits
its trigger-based PPDU in uplink direction to the AP.
[0289] As commonly known, the destination station (the AP) will
send an acknowledgment related to each received MPDU from multiple
users inside the OFDMA TXOP, so that the station 600 may update its
OCW contention value accordingly.
[0290] Although the present invention has been described
hereinabove with reference to specific embodiments, the present
invention is not limited to the specific embodiments, and
modifications will be apparent to a skilled person in the art which
lie within the scope of the present invention.
[0291] Many further modifications and variations will suggest
themselves to those versed in the art upon making reference to the
foregoing illustrative embodiments, which are given by way of
example only and which are not intended to limit the scope of the
invention, that being determined solely by the appended claims. In
particular the different features from different embodiments may be
interchanged, where appropriate.
[0292] In the claims, the word "comprising" does not exclude other
elements or steps, and the indefinite article "a" or "an" does not
exclude a plurality. The mere fact that different features are
recited in mutually different dependent claims does not indicate
that a combination of these features cannot be advantageously
used.
* * * * *